That’s true, but it requires a certain attitude to the Light, something that all races (except the Tauren) have apart from the Zandalari, who almost view the Light as something arbitrary.
Except that ‘holiness’ is not as flexible as you think it is. It doesn’t depend on the perceiver, but on an objective condition, i.e. the Paladin does not see the Light merely as a tool but as something intrinsically valuable.
This is also the reason why Paladins are what they are; they are not agents of justice because they want enforce their own vision of justice, but because they want to deliver the justice of the Light. Paladins are, in a way, interpreters of the Light, like judges are interpreters of the law in a society with a civil law system. There are also Paladins who are misguided in that, but since they still have that relation with the Light we can still call them Paladins.
You can argue that the Prelates interpret the will of the Loa, but I reply that exactly that makes them something different than the Paladins – Paladins serve nothing else than the powers they use, while Prelates worship the Loa instead of the Light.
Note that I am doing the exact same thing as you did, I look at the various races of Azeroth who can be Paladins, and describe their attributes. Apart from the debatable Tauren, all other Paladins have developed a relationship with the Light (even the Blood Knights), unlike the Zandalari Prelates, who use the Light merely as a tool.
Prelates are interesting in their own right, not as a Paladin.